This invention relates to systems that measure parameters of a fluid.
The sampling of fluid within a system allows the fluid to be tested for concentration of various substances. Typically, the fluid within an environmental system such as the air in an office building or a hospital is monitored to determine the level of pollutants such as carbon monoxide and carbon dioxide in the system. The information obtained during the monitoring can be used to control a heating ventilation and air conditioning (HVAC) system, e.g., to control indoor air quality (IAQ). In one approach to monitoring IAQ, remote sampling systems are connected to various locations in the system by a network of tubes that shunt fluid to a central location where in-line measurements are made on air components. In other monitoring systems, sensors are distributed throughout a building and electronically communicate with a central controller.
In addition to monitoring the level of pollutants, it is desirable to monitor and control the flow of pollutants such as carbon monoxide (CO), carbon dioxide (CO.sub.2), odors, and dust by monitoring and controlling the fluid flow within the system. Thus, the pressure within the system, especially the pressure differential between two locations within the system, often is measured to determine fluid flow within the system. For example, pressure differentials across the external walls of a building are important to maintain a positive indoor pressure, especially at the lower levels of a building where negative pressures are more likely to form due to the buoyant force of heated air. The positive indoor pressure prevents air from entering the building as a draft and forces outdoor air to be introduced through the HVAC system where it is conditioned properly and filtered. Because pressure differentials within a building dictate the flow of air, they are important in the control of contaminants in sterile environments as in hospitals. In addition, pressure differentials across the wall of an air duct can be used to determine volumetric airflow within a component of an environmental system.
A typical method for measuring pressure includes connecting pressure sensors to various locations within the system and comparing the pressure measurements to determine the magnitude and direction of fluid flow. A set of sensors may be used at each location with each sensor being most accurate in a different range.